one approach is to use a thin flat lexan or other plastic cover to protect a mylar surface. thin flat lexan or other plastic would be easy to clean, would have minimal distortion/shading effects, and would be cheap to replace every few years mylar is cheap highly available and an excellent reflector..... just needs protection

benbenben

Ya...sticking thin reflecting film is one option..but the problem is that it is quite messy to stick film onto a curved surface(as the plastic sectors of the paraboloid are curved)...

Vacuum fitting the thin flim to the surface of the reflector - - - the thin flim is stretched as a flat surface across the face of the reflector and then a vacuum is drawn in the void area formed by the dish and thin flim. As the vacuum increases the thin flim is drawn tightly to the surface of the parabolic shaped surface. Using a shop vacuum cleaner to draw the vacuum will work surprisingly well.

A guy in sweden made a "dish" by using 2 troughs. The focus of the primary trough falls on the directrix of the second one. http://kmr.nada.kth.se/files/pointfocus/PointFocus/PointFocus-Discovery.jpg It is hugely easier to make 2 troughs than to make 1 dish and it is hugely easier to cover them with reflective material too. The focus is in a completely different place that in the dish situation. And it may be that if things are configured right you can do equatorial mount and single axis tracking. (something you cannot do with a parabolic dish. http://www.youtube.com/watch?v=dfFuyUbdEOE&NR=1 I know it is hard for people to turn when they are already driving towards their prefered solution, but perhaps it is time to turn and evaluate the 2 trough idea? Brian

The problem in using trough is that focus will be a line thereby loses efficiency(yet I agree easy to build compared to dish). And using more than one reflectors means again loss in the efficiency. This even leads to increase in the capital costs as more components are involved.And one more interesting point to note looking at the picture is that: The efficiency of the system depends even on the pointing angle of the reflector towards the Sun, in the Dish concentrator, the deviating angle will be less than 5 degrees as the focus will be a point (covers small space compared to line). if the focus is line and if we keep another mirror/lens on the top, this might demand the change in the pointing angle of the first mirror towards sun which means a major impact on the efficiency of the whole system. Am trying my best to understand this... Thanks a lot for everyone who is helping me out.... There are various Physical Vapor deposition coating processes available..someone could consider even them.. Unfortunately I have no much knowledge about them. Suggestions in that aspect are welcome....

You don't say what the purpose of the concentrator is. In some applications a single trough may be considered ideal. In the Pointfocus files the second mirror of one setup brings the rays to a point focus which could be offset and used with the described mounting for tracking .

You HAVE to look at the image. It is 2 troughs in combination.. They move together. And they focus the light to a POINT just like a dish does. Depending on how you allign the first trough with the sun, you might get a getter deviating angle too. It is disappointing that people rush in and blow something away without even looking at it. Brian

I completeky agree with you from the optics point of view: 1 element is more interesting than 2.

I presume you also performed some 3D optical simulations and optimizations.

Hi,

Please visit this site they are mfg. the plastic reflectors for solar dish. http://www.reflectechsolar.com/product.html.

Suresh Sharma.

if your going to use a thin film covering, then you you should just get thin film pv and avoid the head aches. I do not know if you can coat a parabolic with thin film pv? might work well..

We did some trials on 4 foot dia parabolic dish many years back. We just stuck thin aluminum foil on the surface using araldite adhesive. Since it was meant only as a concentrator and not an optical imaging objective small imperfections were ignored. At the focal point thermocouples recorded temperatures above 1200 Deg C at peak insolation. We did not do any major study on the quantum of energy collected. At Bangaloe (13 deg North) the peak insolation is about 800 W/sq.mtr.

Hello All,

This blog vein has been quite interesting and has provided some good information that I could possibly use in my thermal solar collector project.

In my case, I'm using NASA-surplused evacuated glass tube solar collectors. I was thinking of building some trough-type concentrators using longitudinally-sectioned 4 or 6-inch diameter PVC pipe together w/ UV-stabilized aluminized coated mylar film adhered to the inside of each pipe trough. I'm trying to do this as cheaply as possible, but want to get as much bang out of the system for my hard won Bucks. I want to stayy away from aluminium and aluminized steel just for the sake of cost and ease of fabrication......in other words the KISS Principle applies here Big Time for this DIYer.

Does anyone know what type of adhesive would be appropriate to use to adhere the mylar film to the inside of the PVC troughs which would be long lasting and compatible with both mylar and PVC? Hopefully a spray-type adhesive right out of the spray can, or if not, one where I can apply it with either with one of my 5 Iwata Airbrushes or a larger airgun.

Also, is there such a thing known as a "Lineal Fresnel Lens" that I could install atop the troughs in order to increase the solar radiation gain as well as protect the evacuated tubes and the mylar film from degradation due to exposure to the environment? I don't want to use a round Fresnel Lens as that would be impractical. I need to avoid localized hot spots or concentration spots and would rated keep the focused beam of concentrated light in a linear line applied to the excavated collector tubes (inner tube has gold coated surface).

Any other ideas?????

TIA good folks! Have a super duper weekend!

Signed, Da CaptMoosie

There is also a winston "W" collector that you could look into. It collects light from a very wide angle of incidence. Winston is a bit famous and his design is out of patent now. More info in the fossil freedom group at yahoo.

Lineal fresnel lens do exist. I saw a short presentation on National Geographic Channel just yesterday about what you are discussing. I do suspect that with a solar "thermal" system that significant problems with temperature of any form of plastic or flexible silcon lens would be encountered. I suspect that you would be foreced to use a tempered glass lens as a minimum.

Thanks nukesub629, I was afraid that they didn't exist, or am I applying the name Fresnel incorrectly to another type of lens? For some reason I remember some sort of semi-cirular lens (that could possibly be placed over a trough) that had many parallel lines or grooves in it that were aligned along its' longitudinal axis that helped channel or direct the suns rays almost like a Fresnel lens. I think I saw such a thing many moons ago in an Edmund Scientific catalog while I was wee teenager back in the old 70's. Now I'm dating myself! LOL/UUGGHHH!!!!

Yes, the encapsulated glass collector tubes will get plenty hot enough, with the internal copper heat pipe and bulb reaching up to about 350 degrees F. Of course, any plastic in contact with it will probably melt, unless its made of Bakelite. I was looking for a concentrator lens to place above and not in contact with the tubes or the mirrored concentrator below the tube......just want to gather more radiant energy on a per square basis, that's all.

BTW, like the Username! In reference to USS Daniel Boone, SSBN 629 possibly???

Yes, the reference is to the Boone, I was an M Div-er on the Boone for almost 6 years between 1973 and 1979.

Your description of the lens is very close that shown on TV. Basically a flat plastic plate with one smooth side and the opposite side cut with prisms. The application as shown was for focus of solar radiation onto a line of thin flim solar cells. The cells were arranged in the focal point, minus a few cm to spread the concentrated energy over the width of the cells. Additionally, to place the cells at the focal point of the mirror would cause extremely high temperatures on the cell surface.

Why do you want to combine two types of focusing devices? The parabolic trough does focus the radiation along its focal axis. If a Fresnel zone plate is at the top, that would also focus the radiation to the tube but produce a diverging beam to the rest of the trough, which cannot focus this to the focal axis. Better option is to use the trough with a aluminum foil or mylar film reflector. Low cost two component epoxy brushed on to the pvc surface roughened by scotchbrite should give a long lasting bond. If the aim is to produce just hot water none of it is needed. Concentrating the radiation only increases temperature. The incoming energy is fixed by the area exposed to the radiation. In the late '60s MIT produced a low cost design of trough collector with vacuum tube technology similar to your concept to melt Sodium Nitrate to work as a hot plate that used the latent heat of fusion of the crystals for use as a domestic hot plate.

Hello bioramani,

Perhaps you're right about the Fresnel dispursing the focused rays in the wrong fashion. I was aiming to gather more of the sun's rays somehow.

I'm using 2.125-inch OD evacuated borosilica (sp?) glass tubes that are 46-inches long, give or take. The inner tube has a gold film coating on it. I envision that they will be spaced at 6-inches apart. PVC troughs made from cutting a 4 or 6-inch diameter PVC pipe will be lined with reflecting (aluminized) mylar film will be placed directly below the glass tubes. My system will be used to heat domestic hot water and heat the house during the cold months here.

With some sort of clear plastic lens or clear plastic cover I was hoping to pickup additional surface area, and hence an increase in collecting the radiant energy. The object of this exercise is to produce a marked increase in BTU ouput from the heat pipe and heat bulb located inside each evacuated tube. The more heat produced the better....then I use less home heating oil and lessen the financial strain on my budget during the winter months, which BTW, can be pretty extreme here in upstate NY.

I'm plan on using a small amount of MEK as the fluid in each heat pipe. Also, I want some sort of clear plastic cover over the troughs to do the following: (1). Protect the evacuated glass tubes from damage, (2). Protect, and to prolong the life of the the mylar film (even if it is UV stabilized) from the elements. We receive a lot of snow, freezing rain, sleet and hail here during the harsh winter months. We get good sized hail during thunderstorms here the remainder of the year, and (3) Ease of cleaning the entire assembly.

Basically, I don't want to have to replace the expensive mylar film every few years. As long as I can protect it I think I won't be replacing it so often.

Dear Captmoosie, Take a look at this: http://www.nuetechsolar.com/products/etcmodel.asp I have a 25 gallon version of this on the roof. It cost me the equivalent of USD500 including installation.We have stopped using electric power on this count. Earlier I had made a much cheaper collector using GI corrugated sheet with regular 3/4" GI pipes welded into the corrugations, the whole assembly painted with ordinary matte black board paint. The collection area in this was about 16 sq.ft. about the same in the new vacuum tube one. My home made unit cost me the equivalent of USD150. It worked satisfactorily for 7 years. It still was when I dismantled it to put in the vacuum tube one, succumbing to the lure of technology. I do not see much difference in the total collected energy between these two in use. You do not have to bother too much about solar hot water generation. It is very forgiving. Of course, I am at 13 deg North in perennial summer. The peak insolation is about 80W/sq.ft.

Hello nukesub629,

Nice to have met you, and thank you for serving our country in such a difficult job. I'm former US Army myself, but that's besides the point. When I saw your moniker I immediately thought of the Boone. During the years that you served on her I was teenager building plastic scaled models of ships, airplanes, cars and whatnot. One of the models that I had built back then was the USS Boone! I heard that the Navy decommissioned her sometime in the mid-90's if I'm not mistaken. Sad the see sure a great ship disappear from the active register! She was an Ethan Allen class boat wasn't she? I may be wrong on that account, since it's been so many years between the model build and today.

Where I grew up in upstate NY (Burnt Hills) was about 6 or 7 miles south of the Kesselring Site which was run by the USN, GE and the DOE. No doubt you probably pulled a training tour of duty there like most USN nuke sub engineers. After graduating from engineering college I worked for a firm doing consulting work at that site as well as KAPL in Niskayuna. I used to work with USN personnel all the time in my work. It was a pretty kewl site to visit, but security was so freaking tight!!!! Nothing like security folks breathing down or looking over your shoulder all the time!!! LOL Worse thing was filling out the security clearance paperwork, all of which had 5 copies with every T crossed and every i dotted. And this was back when we used old electronic typewriters and hope the secretary wouldn't screwup and do a typo!!! If she did, it was back to square one again! FRUSTRATING TOP SAY THE LEAST!!!!

Later on after getting married, my X and I owned a two-family house in Amsterdam where we usually rented the upstairs apartment to Navy families. I got to know a lot of good people!!!!!

In regards to the lens that you saw on the show, do you remember what type of lens they called it, if it even has a name? From your description, it sounds exactly what I remember from long ago and am now looking for. One question more: was the outside surface curved upwards like a vault or was it laying down flat?

Hello CaptMoosie;

Yes, the Boone along with all of the other "41 for Freedom" were decomissioned and recycled through the "submarine recycling program". Boone was one of the first boats to be decommissioned, exactly why I do not know, probably because of a spent reactor. She was also one of the better boats in the fleet, and I would think that a lot of the equipment from her ended up on the newer boats being built around that time. The Boone was a 627 Class - James Madison Class boat, with a GE engineeroom. My early days in the Navy were on the West Coast, Nuc School at Mare Island, then Prototype in Idaho . . . but did go to welding school in New London. Then to the Boone in Charleston, SC (forward based out of Holy Loch). The subservice was a tough job, but I got a good education too.

Although I was familiar with the KAPL labs in NY I never spent any time there at all, at least not while in the Navy. I did during the mid-1990's work at Fitzpatrick Nuclear Station, near Oswego for about 2 years. Actually worked at 21 different commerical plants all around the US from 1980 through 2000. I worked mostly with plant operations doing engineering work and some training of control room operators.

My humble and heart felt respect for your service to our country and freedom of all. The military asked for a lot and then took more.

With respect to the lens, yes it was held in a bow fashion over the top of the cells. The specific purpose was to build an orbital power plant.

Check out this picture at the following link:

http://www.instablogsimages.com/images/2009/01/19/solar_DaeQI_5638.jpg

Happy to help with your project in anyway that I can.

George

Hello nukesub629 (George),

Wowsers, you sure did get a lot of training in the Navy! I wish I knew more about the submarine service, but all the USN personnel I dealt with were very tight-lipped about what they did, and rightfully so! I don't know if I could have ever gotten used to being shut-up inside a steel tube underwater for the duration you guys did...I tend to get claustrophobic to the nth degree!!! LOL No problem jumping out of perfectly good airplanes with a chute while I was in Airborne and later Rangers, but no tiny closets or underwater steel tubes for this guy!!!! OH NO NO NO WAY!!!! yikersss!!!!

Agreed that the military took too much. after 14 years service and two conflicts later I was spent....and my X wanted me out of the Reserves after DS in '91 or else.....just blackmail through and through w/ small kids involved....So, I ended up divorcing good 'ole "T-Rex" anyhow a decade later!

So, did the Navy actually cut up the Boone, or is she in mothballs somewhere in a Reserve Fleet? Probably the former in accordance with the SALT II agreements eh?

That's pretty kewl that you worked at the Fitzpatrick plant up in Oswego. My brother-in-law Peter had worked up there for a while in the 1980's for a private consulting firm. If fact he's worked all over the US just like you on numerous nuke plants. I think they did repairs on the hot pipe works at Oswego, and maybe was involved somehow removing the spent fuel rods. I'll have to ask him next time I see him. Now, he works for Lockheed Martin at KAPL. I always kid him and my kid sister that she has no trouble finding him in a dark bedroom 'cause he glows!!! LOL

yes yes yes, that's the lens that I was thinking about all along! Where did you find that pic? Who makes them, and what are they called? Any URL links? Pretty kewl stuff......the entire gizmo looks like it's on a sun tracking frame if I'm not mistaken.

Yep, I went to school for a little over three years total. That was just getting to the boats as a nuclear power plant operator/welder.

The Boone along with so many other boats, well over 100 now look like this:

http://home.flash.net/~tomj/tunny/chop/chop.htm

Here is an interesting link where someone has gone to a lot of trouble to research and post various patents. One of the articles addresses the fresnal lens.

http://www.rexresearch.com/solrfurn/solfrnpat.htm

George